Reward-learning and the novelty-seeking personality: a between- and within-subjects study of the effects of dopamine agonists on young Parkinson's patients

Abstract

Parkinson's disease is characterized by the degeneration of dopaminergic pathways projecting to the striatum. These pathways are implicated in reward prediction. In this study, we investigated reward and punishment processing in young, never-medicated Parkinson's disease patients, recently medicated patients receiving the dopamine receptor agonists pramipexole and ropinirole and healthy controls. The never-medicated patients were also re-evaluated after 12 weeks of treatment with dopamine agonists. Reward and punishment processing was assessed by a feedback-based probabilistic classification task. Personality characteristics were measured by the temperament and character inventory. Results revealed that never-medicated patients with Parkinson's disease showed selective deficits on reward processing and novelty seeking, which were remediated by dopamine agonists. These medications disrupted punishment processing. In addition, dopamine agonists increased the correlation between reward processing and novelty seeking, whereas these drugs decreased the correlation between punishment processing and harm avoidance. Our finding that dopamine agonist administration in young patients with Parkinson's disease resulted in increased novelty seeking, enhanced reward processing, and decreased punishment processing may shed light on the cognitive and personality bases of the impulse control disorders, which arise as side-effects of dopamine agonist therapy in some Parkinson's disease patients.

Figure 1

The feedback-based probabilistic classification task. (A) On each trial, the participant saw one of four stimuli and was asked whether this stimulus belonged to category A or B. (B) For some stimuli, correct responses were rewarded with visual feedback and 25 points winnings, whereas for others, incorrect responses were punished with visual feedback and the loss of 25 points.

Figure 2

Results from the feedback-based probabilistic classification task. The never-medicated Parkinson's patients (nm PD) outperformed the recently medicated patients (m PD) in the punishment condition, whereas the recently medicated patients outperformed the never-medicated patients in the reward condition (P < 0.001). Data are mean, error bars indicate standard errors.

Figure 3

Correlations between novelty seeking and reward learning in controls (black), never-medicated Parkinson's patients (blue) and recently medicated patients (red).

Figure 4

Correlations between harm avoidance and punishment learning in controls (black), never-medicated Parkinson's patients (blue) and recently medicated patients (red).

Figure 5

Results from the feedback-based probabilistic classification task at baseline and at follow-up when Parkinson's patients (PD) received pramipexole and ropinirole. In reward learning, performance in the unmedicated baseline condition (base) was signifcantly worse than in the medicated follow-up condition (follow), whereas in punishment learning, performance in the unmedicated condition was significantly better than in the medicated condition (P < 0.001). Data are mean, error bars indicate standard errors.